By Sam McKeith

A major cruise ship has made its way back into Sydney Harbour after a desperate early morning search for a passenger who went overboard ended in tragedy.

Water police battled big swells on Monday in the search for the passenger from P&O’s Pacific Adventure after a person-overboard alarm was sounded on the ship at 4am.

More than six hours later, officers from NSW Police’s Marine Area Command retrieved a man’s body from the water.

An investigation has been launched into the incident and a report will be prepared for the coroner.

P&O said its vessel, which has capacity for more than 2600 passengers, had been cleared to return to port following the search, which took place about 18km outside Sydney Harbour.

“We thank guests for their care, understanding and patience on what’s been a distressing day for guests and crew,” a company spokeswoman said.

She said the family of the dead man was “being cared for by our onboard team”.

The Elvis-themed cruise made its way under the Harbour Bridge on Monday afternoon en route to White Bay Cruise Terminal, where it had been due to dock in the morning after a three-day cruise of the NSW coast.

Marine Area Command head Joe McNulty earlier said swells of up to five metres forced authorities to rely on heat-seeking technology in the search.

Authorities had hoped to find the passenger alive given a life ring from the cruise ship was yet to be recovered at the time.

The Pacific Adventure’s next scheduled departure, for a four-day trip to Queensland, has been delayed until Monday night.